1. Technical Field
The present disclosure relates to an internal combustion engine having a selectively engageable rocker arm with a device for positioning the rocker arm while disengaged.
2. Background Art
Variable displacement or displacement on demand engines offer the performance of a larger displacement engine with improved fuel economy associated with a smaller displacement engine by selectively activating and deactivating one or more cylinders in response to driver demand and current operating and/or ambient conditions. One strategy used in mechanical valvetrains for selectively deactivating cylinders is to disengage or unlatch at least the intake rocker arms and associated intake valves of selected cylinders. To transition to a higher displacement operating mode, the rocker arms engage or latch to actuate the associated intake valve, which requires alignment of the latching mechanism and the associated rocker arms. Additional mechanical lash or clearance may be added to the system to accommodate manufacturing and assembly tolerances and valvetrain component wear while ensuring proper alignment and latching. Although suitable for some applications, the additional lash added to the system to ensure reliable alignment and latching may result in undesirable noise.
Hydraulic lash adjustment mechanisms are used in various types of mechanical valvetrains to compensate for manufacturing and assembly tolerances and component variations due to temperature changes and wear. In variable displacement engine applications having rocker arms that are selectively coupled and uncoupled to activate and deactivate cylinders, movement of the lash adjuster may result in a corresponding change of position of the latching alignment hole. As such, to ensure proper latching across the range of motion of the lash adjuster under varying operating conditions while also accommodating valvetrain design tolerances, the actuating cam profiles are modified for at least the selectively deactivated cylinders, resulting in design compromises with respect to various factors, such as manufacturing cost and complexity, noise, reliability, and durability, for example.